Electromagnetic actuators are electrically controlled mechanical actuators and serve to transform electrical energy into mechanical energy or movement. They include an electromagnet having terminals for applying an electrical voltage thereto, and a movable anchor that can be displaced by the electromagnet. Electromagnetic actuators are used, for example, in relays for switching electrical contacts, or in magnetic valves for opening and closing the valves. Magnetic valves are, for example, used as injection valves in internal combustion machines, or for controlling liquid flow in a clutch system.
The electromagnetic actuator is switched on by applying an on-voltage at its input terminals and is switched off by applying an off-voltage at its input terminals. For switching the electromagnetic actuator, i.e., for applying the on- and off-voltages, a semiconductor switch, such as a MOSFET or an IGBT, may be used. The semiconductor switch is connected in series to the electromagnetic actuator, with the series circuit being connected between supply voltage terminals. Some systems, such as internal combustion machines, employing electromagnetic actuators require an exact control of the activation and deactivation times of the actuators. One problem arising in this connection is a delay time between the time of electrically switching the actuator and the time when an activation state changes. The time when the activation state changes is the time when the actuator “mechanically switches” the anchor, i.e., the time when the anchor is displaced.
In fluid systems having an electromagnetically actuated valve a flow sensor may be employed to detect a change in the activation state. The flow sensor measures a gas or liquid flow through the valve and, therefore, provides information on the times of opening and closing the valve. However, providing a flow sensor increases the overall costs of the system employing the electromagnetic actuator, and increases the number of mechanical components in the system.
There is therefore a need for exactly determining a change in the activation state of an electromagnetic actuator at low cost.